Centripetal acceleration method and apparatus



Nov. 28, 1967 M. G. HUNTINGTON CENTRIPETAL. ACCELERATION METHOD ANDAPPARATUS 8 Sheets-Sheet l Original Filed July 29, 1964 BY '16, my, wwz

Nov. 28, 1967 M. G. HUNTINGTON 3,355,382

CENTRIPETAL ACCELERATION METHOD AND APPARATUS original Filed July 29,1964 8 sheets-sheet 2 @Mm um ITW Nov. 28, 1967 3,355,382

CENTRIPETAL ACCELERATION METHOD AND APPARATUS MG. HUNTINGTON A 8Sheets-Sheet 5 Original Filed July 29, 1964 INVENTOR Maryam u'dolz#uni/gior 8 Sheets-Sheet 4 INVENTOR 6 A ORNEKSY NOV- 28, 1967 M. G.HUNTINGTON CENTRIPETAL ACCELERATION METHOD AND APPARATUS original FiledJuly 29, 1964 NOV- 28,` 1967 M. G. HUNTINGTON 3,355,382

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CENTRIPETAL ACCELERATION METHOD AND APPARATS Original Filed July 29,1964 8 Sheets-Sheet 6 F: wn 75e FL ux gaL/day/fg? 14770 OFC'NTR/PETHLACCELEKT/A/ 7'0 GRHI//TY F: GALLO/V5 0F WATER IVENTOR ORNEYS Nov. 28,1967 M. G. HUNTINGTON 3,355,382

CENTRIPETAL ACCELERATION METHOD AND APPARATUS Origilnlr Filed July 29,1964 8 Sheets-Sheet '7 GNN mm m T r N N 6 R E w o c v r H m w M 7 h M mM 0 wm B 0.

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CENTRIPETAL ACCELERATON METHOD AND APPARATUS 8 Sheets-Sheet 8 OriginalFiled July 29, 1964 United States Patent O 3,355,382 CENTRIPETALACCELERATION METHD AND APPARATUS Morgan G. Huntington, Galesville, Md.,assignor to Waterdrink, Inc., Salt Lake City, Utah, a corporation ofNevada Continuation of application Ser. No. 385,964, July 29, 1964. Thisapplication Oct. 22, 1964, Ser. No. 418,574 22 Claims. (Cl. 210-22) Thisapplication is a continuation of applicants copending application Ser.No. 385,964 filed on July 29, 1964, now abandoned.

This invention relates to the winning of fresh water from inorganic and/or organically polluted solutions by reverse osmosis and also relates tothe separation of light molecular weight solutions from heavy molecularweight solutions by pressure modified dialysis. This inventionparticularly relates to a method of and apparatus for preventing theexcessive concentration of solute and for preventing the excessiveaccumulation of precipitates against the osmotic or dialytic dividersurface at any water flux and at any primary solution circulation rate.

This invention also relates to a method of preventing suspended solidsfrom contacting the osmotic membrane, and/or dialytic membrane surface,thus eliminating the necessity for clarifying incoming turbid solutionsin order to avoid the encrustation, blinding and/or erosion of thedividers by insoluble matter.

This invention further relates to a method of forming and supportingosmotic and dialytic membranes which affords an incomparably largeeffective water-permeable surface in proportion to the total volume ofapparatus.

This invention also relates to a method of rotating the membranesupporting assembly in such a manner that liquids and suspendedparticulate matter are subjected to constant acceleration greater thangravity in a direction away from the effective fluid-dividing surface,thereby continually forcing concentrated solution and particulate matteraway from the fluid-dividing surface by centripetally induced convectionso that both the solvent flux and solute diffusion through thesemi-permeable divider become independent of the solution circulationrate past the divider surface.

This invention also relates to the employment of centripetally inducedconvection to minimize the difference of solute concentration across theosmotic divider and to supplement the solute diffusion rate on thesolution side of the membrane by mass transfer and to retard the solutediffusion rate on the solvent side of the membrane.

This invention also relates to the improvement of mernbrane solutionpermeability in reducing the degree of pressure deformation of themembrane body by lowering the over-all required hydraulic pressureapplied to the surface of the membrane for any given solvent flux.

This process also relates to a method of concentrating dissolved organicmatter from raw sewage and/or dissolved inorganic salts from sea waterwherein precipitated compounds and other particulate matter, which mightbe pressed against the membrane surface, are repeatedly freed from themembrane surface by pressure waves, such as those induced by modifiedwater hammer, periodically exerted against the water side of themembrane or by momentarily reduc'mg the applied solution pressure.

The process of separating water from saline and/ or organic solutions byreverse osmosis consists of forcing the solution, at a pressure inexcess of its osmotic pressure,

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against a supported, molecular and ion-restraining, semipermeabledivider that, under optimum conditions, passes water more freely thansolute. The divider can be an osmotic membrane composed principally ofcellulose acetate, as disclosed in U.S. Patents Nos. 3,133,132 and3,133,137 for example, which passes water and limits the transport rateof most inorganic and organic solutes, the mechanics of which are notyet satisfactorily explained, or the divider between solution and watercan be a hydrophobic porous filter which is impermeable to solutions andto water but permeable to water vapor. In this latter case the processis referred to as vapor gap reverse osmosis.

The osmotic pressure between water and sea Water, for example, whenseparated by a water permeable and ionrestraining membrane, is wellknown and has a value of about 370 pounds per square inch absolute. Theprinciple of extracting water from both inorganic and organic solutionsby exerting a pressure on the solution somewhat greater than the osmoticpressure has long been recognized as physically possible andthermodynamically advantageous over other water-extracting principles.However, mechanical deficiencies have heretofore prevented thedevelopment of commercially practical sewage treatment and waterrecovery processes involving. reverse osmosis techniques.

When a non-volatile non-electrolyte is dissolved in a liquid, the vaporpressure and the freezing point are lowered, the boiling point is raisedand the osmotic pressure between lsolution and solvent manifests itself.These four colligative properties of non-electrolyte solutions dependupon the number of solute molecules present.

The osmotic pressure between a solvent separated by a Semi-permeabledivider from a dilute solution of a nonelectrolyte solute obeys therelationship,

1r=nRT, or 1r=cRT where:

c=n/V is the concentration of solute in moles per liter; R is theuniversal gas constant; T is the absolute temperature.

However, when dealing with solutions of electrolytes, these colligativeproperties are amplified by factors which, in dilute solutions, approachthe number of solute ions per mole of solute present. The Vant Hofffactor, i, which modifies the osmotic pressure as 1r=icRT, is defined aswhere ir is the observed osmotic pressure of a solution of anelectrolyte; 1ro is the osmotic pressure calculated from 1r=n/ VRT=CRT.

Obviously, as the solution becomes more dilute, factor i approaches thenumber of ion-s per mole, which would become 2 in the cases of NaCl andKCl and 3 for BaC12.

That factor z' decreases as the solution of an electrolyte becomes moreconcentrated is explained in terms of the inten'onic attraction theory.At saturation of a solution by an electrolyte, evidently the interionicattraction is very high and the osmotic pressure is much less thanw-ould be predicted if all ions were considered as single particles andif the osmotic pressure were extrapolated as a straight line and as arst power function of the solute concentration. This is illustrated inFIGURE 8.

When solutions containing different concentraitons of solute areseparated by a semi-permeable divider, solvent moves across the dividerfrom the lower concentration and dilutes the more concentrated solution.At the same time, the solute diffuses through the semi-permeable dividerto enrich the solution of lower concentration.

Although the movement of solvent across the divider can be halted oreven reversed by exerting a pressure on the more concentrated solutionequal to or greater than the difference in osmotic pressure, the diusionof solute is practically unaffected by change in hydraulic pressure, bythe direction of solvent flow or by the rate of forced solvent flux.

In the process of reverse osmosis the solution pressure is maintainedgreater than the osmotic pressure so that solvent flow is reversed.Whatever the actual mechanics of solvent and solute transport, in trueosmotic membranes, solute leaves the solvent at or near the semi-permea'ble divider surface and thereby concentrates at the phase interface.The rate at which the solute is brought to thedividertsurface is afunction of the rate at which solvent is -forced through the divider.

The salient, limiting factor in separating water from brine by reverseosmosis and using a semi-permeable membrane, for example, is the problemof removing the Vconcentrated solute from the membrane surface. Theconcentrated solute at the membrane boundary layer can ordinarily betransported away from the phase interface by two means only: (a) bydiffusion -back into the brine, and (b) by diffusion through thesemi-permeable membrane. In either case, thev quantity of solutetransported per unit time is proportional to the area and to theconcentration gradient in the direction of diffusion and is expressed bythe differential equation, which is analogous to that for thermaldifr'usivity,

where :weight of solute transferred t=time in seconds D=diffusioncoefficient, crn.2/sec.

A=area of diffusion front, cm2

Czconcentration in grams/cc.

Z=distance measured in the direction of diffusive flow,

Integrating the above equation, we obtain W=weight of solutiontransferred, gm./sec. U=overall diffusion coefcient,

g./sec. ma OI CUL/SSG.

A=area of diffusion face, cm2 AC=plogarithmic mean of the concentrationgradient,

From the above expression, it is clear that the higher the concentrationof solute at the boundary layer, the more rapid the transport of solutethrough the membrane into the product solvent, as is shown in FIG. 6,which is derived from the actualperformance of UCLA membrane No. 1,described in UCLA Report No. 63-22, Department of Engineering,University of California, Water Resources Center, Contribution No. 74(May 1963). Also, the more nearly saturated is the bulk of the solution,the slower is the rate of diffusion of concentrated solute back intosolution and away from the phase interface.

The water flux, or rate of solvent flow through the osmotic membrane,may be expressed by F is the water flux (water production per unitarea).

AP is the pressure drop across the membrane.

1r is the osmotic pressure difference across the membrane.

K is the membrane constant determined by properties of the particularmembrane.

solute concentration against the membrane when oper-V ated athigh waterflux is the actual deposition of compounds precipitated from theconcentrated solution upon the membrane surface which further reducesthe membranes permeability to water. Yet another boundary layer effectstems from the diculty in forming absolutely perfect membranes, most ofwhich contain some defects in the form of actual holes. Because thesolution normally reaches its highest concentration at the membranesurface, any physical leak must allow the direct passage ofV highlyconcentrated solution and, therefore, the adverse effect of suchmembrane imperfacti'on is greatly magnified.

The boundary llayer conditions noted above which adversely effect theproduction rate of Water through osmotic membranes are at least equallyserious in the functioning of hydrophobic filters which provide a vaporgap between solution and Water in the similar process of vapor gapreverse osmosis. Vapor gap reverse osmosis is thought to differ fromosmotic membrane process mechanics principally in that a poroushydrophobic filter replaces the membrane, and phases change from liquidto water vapor and back to water. The porous filter of certain pore sizeand pore volume is permeable to water vapor but impervious to water andto solution even when pressurized well above the osmotic pressure. Suchhydrophobic filters, the pores of which are filled with water vapor andconstitute the Vapor barrier, have served to demonstrate the process astechnically feasible but the water flux rates are discouragingly small.

On the other hand, osmotic membranes have been de- Veloped which arepermeable to distilled water in the order of one to seventy gallons perday per square foot under pressures of 500 to 1500 pounds per squareinch. Certain semi-permeable dividers can reject a high proportion ofthedissolved salts under laboratory test conditions. Product rate has, sofar, been inversely propotional ,to the initial salinity and commercialscale demonstration of sea water demineralization has'not so farmaterialized.

Several pilot plant operations incorporating the principle of reverseosmosic have recently demonstrated an operable process which cancontinuously produce potable Water from brackish water (i.e. less than5000 ppm.) at rates comparable to those obtained in Vthe laboratory.However, in all processes so far demonstrated, the energy consumption isin the order of three to five times that required to pump the brackishWater to system pressure and about 10 times the theoretical minimum of2.9 kwh. per 1000 gallons of water from sea water. Successful andcontinuous desalination of sea water by reverse osmosic has yet to bedemonstrated, even on a pilot plant scale.

The energy required to win fresh water from saline sources by reverseosmosis, whether by membrane solution mechanics or by vapor gap phasechange mechanics, is the work necessary to pump the incoming stream tosystemv pressure, divided by the. yield and by the severalV mechanicalefficiency factors. For example, to pump 1000 gallons of sea water to apressure of 1500 pounds per square inch theoretically requires about10.8 kilowatt hours of energy. Then, if the water yield factor is takenas 0.33 and the motor and pump elciency factors are assumed to be 0.8each, the gross energy requirement becomes:

10.8 kwh. 0.33X0.SXO.8

Pump etiiciewv Motor eciency Potable Water yield or 51.1 kwh. per 1000gallons of product water.

Obviously, there are presented these possibilities of processimprovement in respect to energy demand for sea water desalination:

(a) Improved yield of desalinated and decontaminated Water, whichimplies a higher solute concentration in the failing solution.

(b) The optimization of pump and motor design for the particularservice.

(c) Reduction of the practical system pressure which can be effected by:

(1) Improved membrane permeability to water;

(2) Increased area of effective membrane surface;

(3) Improvement of the means of removing concentrated solution andparticulate matter from the membrane surface.

(d) Reduce the system pressure drop by:

( 1) Lowering the solution velocity across the membrane surface andthroughout the system generally;

(2) Improving the permeability of the lower part of the membrane and ofthe membrane support;

(3) Providing a means of continuously removing salts, such as gypsum,which may precipitate upon the membrane.

(e) Recovering most of the pumping energy requirement from the highpressure tailing solution by hydraulic turbine directly connected topumps or by some other means.

By effecting all of the more obvious economies, the net energy demandfor extracting water from sea water can be reduced to about 2O kwh. per1000 gallons, or slightly below.

All demonstrated processes for the winning of fresh water from solutionsby reverse osmosis are dependent solely upon the velocity of solutionover the membrane surface for removal of the solute concentrated by thepassage of water through the osmotic membrane. Heretofore, at a givensolution pressure, water iluX has always been proportional to thevelocity of solution across the membrane surface. However, even atturbulent flow and no matter how smooth the surface, some fluid at themembrane surface must approach zero velocity, and dependence uponsolution circulation for the removal of concentrated solute from themembrane surface is unsatisfactory. Such an inherently defectivemechanism cannot give the highest possible water flux because, in thefinal analysis, the rate of solute removal from the membrane surfacemust remain largely a function of diffusion back into solution.Furthermore, high velocity circulation of solution is seriously wastefulof pumping energy.

Therefore, it is an object of this invention to more rapidly and moreeffectively remove concentrated solution and precipitated compounds fromthe membrane surface by forcing mass transfer by convection throughsubjecting the system to constant radial acceleration in a directionaway from the membrane surface and thereby to make the water productionrate independent of the solution circulation rate.

Turbid saline water must be thoroughly clarified before use indemonstrated systems in order to prevent serious erosion of the membranesurface. This is very eX- pensive and impractical, and it is thereforealso an object of this invention to hold the osmotic membrane harmlessfrom solid matter suspended in solutions.

At low temperatures, high water flux and low solution circulation rate,previously demonstrated processes precipitate salts from seawater,particularly gypsum, against the membrane surface and thereby reduce thewater flux. Indeed, when extracting water from sea water by reverseosmosis, it has been noted that a reduction in the volume of brine by aslittle as one-tenth can cause CaSO4-2H2O (gypsum) to precipitate againstthe membrane surface. As these plate-like crystals cover the membranesurface. the permeability of the membrane is reduced and the water fluxfalls accordingly at any given brine pressure. Furthermore, whenoperating an osmotic membrane on sea water at a very high water iiux,the precipitation of salts against the membrane surface ordinarilyrenders the process practically inoperable, despite extremely high brinecirculation rates. It is accordingly an important object of the processof the present invention to prevent precipitated salts from remaining incontact with the membrane surface and to make the operation of reverseosmosis more practical at low sea water temperatures, at high wateroutput rates and at high ratios of salt concentration. A particularobject of the present invention is to prevent precipitated compoundsfrom remaining in contact with the membrane surface by repeatedlyinducing a modified water hammer on the water side of the osmoticmembrane so that the momentary water pressure plus centrifugal forceimparted to the rotary assembly by centripetal acceleration are togethersucient to overcome the force of the solution pressing precipitatedcompounds against the membrane surface.

It is also an object of this invention to permit the actualprecipitation and discharge of selected salts suspended in brine whensalt recovery may be a purpose of the process.

Because plant cost is a direct function of apparatus volume and of theoor space required, it is a further object of this invention to useconcentric, multiple membranes for the reverse osmosis extraction ofwater from solutions.

It is also an object of this invention to recover potable water from rawsewage and to 'concentrate the putrescible substances into a relativelysmall stream in order to facilitate stabilization by conventional means.

Additional objects and advantages of the present invention wl becomemore apparent from the accompanying description and claims, as well asfrom the appended drawings, wherein:

FIGURE 1 is a schematic flow sheet diagram of the process of the presentinvention indicating the major items of equipment, instrumentation andcontrols;

FIGURE 2 is a schematic longitudinal section showing a two-stageconcentric arrangement of osmotic membranes, their supporting structureand fluid flow through the rotating apparatus;

FIGURE 3 is a transverse section through lines 3 3 of the apparatus ofFIGURE 2, showing the concentric arrangement of membranes within a brinepressure shell;

FIGURE 4 is a schematic longitudinal section of a rotating apparatusincorporating two single stage memv branes, both of which reject acommon concentrated FIGURE 6 plots the salt transport across. asemi-permeable boundary as a function of concentration;

FIGURE 7 plots the theoretical ratio of salt concentration in themembrane boundary layer to the salt concentration in the dischargedbrine as a function of Reynolds number for the fluid flow of brine pastthe membrane at various water ux values;

FIGURE 8 is a plot of the approximate values of osmotic pressure as afunction of the ratio of salt concentration in water across asemi-permeable osmotic membrane, as estimated from the Vant Hoff i ofion interattraction;

FIGURE 9 is a How sheet diagram illustrating the 0peration of athree-stage sea water desalination system embodying the presentinvention;

FIGURE 10 plots the estimated ratio of salt in the boundary layer tosalt concentration in the rejected brine against Centripetalacceleration for various water ilux values; and

FIGURE 11 is a schematic end view of a three stage concentricallyarranged Centripetal accelerator.

The following treatment of rotation about a fixed axis is introduced toexplain how the present invention employscentripetal acceleration toforce the convection of denser media away from the solution side of anosmotic membrane, away from the solution side of a vapor gap,hydrophobic filter and away from the primary solution side of a dialyticmembrane:

' When a particle is rotated about an axis, it is acceleratedperpendicularly away from the axis. Such Centripetal acceleration isexpressed by:

a rw2 where a is Centripetal acceleration in feet per second per secondr=particle distance away from the axis `of rotation in a directionperpendicular to such axis w is the angular velocity in radians persecond.

Centripetal acceleration of a particle may also be expressed as:

where a is acceleration in feet per second per second r is theperpendicular distance of the particle from the axis of rotation r.p.m.is rotations per minute.

For example as 900 2: (upm.) a m2 in order that the Centripetalacceleration equal the acceleration of gravity,

900 (r.p.m. )2-32-2 X m or, the Centripetal acceleration of a particleone foot from the axis of rotation, revolving 54.1 times a minute wouldbe approximately equal to the acceleration of gravity.

As a further quantitative example, a particle one foot from the axis ofrotation, revolving 242 times a minute, would be subjected to aninstantaneous acceleration of twenty times the acceleration of gravity.Also, the acceleration of gravity would be multiplied by 100 at 541r.p.m. Furthermore, since force equals mass times acceleration, theinstantaneous force acting to pull the particle away from the axis ofrotation would be respectively, twenty and one hundred times the forceof gravity.

Thus, it becomes clear that the rotation of a cylindrical vessel ofliquid about its longitudinal axis will force the convection ofrelatively dense uids and particulate matter toward the outer wall ofthe containing vessel and that strong convective forces are induced evenat rather moderate rotational speeds. Also, it is clear that the radialacceleration the more rapid will be the outward convection of densersolution.

In the treatment of certain types of solutions and/or under certainconditions, the centripetally modified reverse osmosis process describedabove is extremely effective in diminishing the solute content of suchsolutions. For example, below certain water ux rates there is nosignificant problem of crystal precipitation and the process describedabove works quite effectively.

On the other hand, there are conditions of operation under which saltcrystals must precipitate at the membrane surface and these saltcrystals tend to be held against the membrane surface by the ow ofwaterV therethrough. It follows that only by decreasing the pressuredrop across the membrane can salt crystals so held be released.

The complete release of precipitated compounds pressed against themembrane surface by the ow of water therethrough can be effected in onlytwo ways: (l) either the primary solution pressure must fall to a valueless than the water pressure plus the osmotic pressure across the suremust, momentarily at least, equal or exceed the static pressure of thesolution. It should be obvious that theV solution pressure differencecannot, even momentarily, be less than the centrifugal force tending toexpand the membrane, else the membrane could suffer destruction.V

Because it is impractical to repeatedly reduce the static pressure inorder to halt iiow through the membrane, and because the membrane mightthereby inadvertently suffer rupture by centrifugal force, the processof the present invention provides for the use of water hammer and twoother less rapid means of pressurizing the water side of the membrane asherebelow explained.

The phenomenon known at water hammer is produced by the sudden stoppageof flow within a pipe. When a Lvalve is quickly shut at the downstreamend of a long pipe, the liquid comes to rest progressively due to apressure wave in the system. The pressure wave moves upstream from theclosed valve at the velocity of sound in the liquid medium. When thepressure wave reaches the. upstream end of the pipe, the liquid is atrest through-f leaving the suddenly closed valve would be that of soundthrough water, about 4,700 feet per second.

The increased pressure of water hammer is proportional to the arrestedvelocity of iiow and to the speed of propagation of the pressure wave.This increased pressure is about 60 p.s.i. for each foot per second ofextinguished velocity for two to six inch pipes. Such an increase topressure can be attained only when the valve is closed faster than oneround trip of the pressure Wave.

For a complete treatment of water hammer and its control, see chapter 3,pages 79-80 of Marks Mechanical Engineers Handbook, sixth edition.V

The present invention may employ any one of three methods of momentarilyincreasing the pressure on the water side of an osmotic membrane inorder to halt the ow therethrough and so that the force holding theparticulate matter against the membrane is Overcome by centrifugalforce. The following methods of pressurizing the water side of osmoticmembranes are listed in the descending order of pressure applicationspeed:

(1) Veny rapid closing of the water discharge line, extingnishing thevelocity of efflux and converting the kinetic energy thereof intopressure known as water hammer.

(2) Closing the water discharge line and subsequently admitting highpressure water on the upstream side of the valve.

(3) Closing the water discharge line and allowing the pressure to riseon the water side of the membrane, thereby momentarily stopping orreducing the water flow therethrough. A further effect of repeatedlyraising ehe pressure on the water side of the membrane and/ormomentarily decreasing the solution pressure is to allow the osmoticpressure to back-Hush the membrane with fresh water as may be requiredby operating conditions.

The present invention may be explained in still greater detail throughreference to the appended drawings.

FIGURE 1 is the ow sheet diagram of the process of the present inventionand shows the sequence of Huid iiow and the means of controlling theprocess. Saline water from the sea or from another source is pumped byintake pump 2 through self-cleaning screens 4 into surge tank 6. Thehight pressure system supply pump 8 pumps saline water through systemfeed rate control valve 1t) through iiow meter 12, through high pressuremain 14, entering the radially accelerated membrane assembly 18 atsaline water inlet gland 70.

The brine, concentrated to a salinity determined by the variables ofsystem pressure, residence time at pressure against the osmotic membraneand the membrane characteristic, is discharged from rotating membraneassembly 18 through outlet 20. Brine pressure, up to the maximum outputpressure pump 8, is controlled by brine discharge valve 22. Valve 22 isregulated by salinity meter 24, reading the salinity of the brine indischarge line 26.

The potential energy of the discharged brine may be partially recoveredby hydraulic turbine 2S.

Because the dependable salt rejection by the osmotic membranesconsidered in the present example is taken to be 95 percent of the brinesalinity, two-stage operation is essential if potable water is to be theproduct, i.e., water containing less than 500 parts per million, as willbe hereinafter explained in connection with Table 1. Therefore, withtwo-stage operation, employing two concentric osmotic membranes in thepresently described embodiment of the process of the present invention,salt must also be rejected in the form of a middling brine, which isconsiderably less concentrated than the primary brine, as is illustratedin Table 1.

As illustrated in FIGURE 1, middling brine is discharged from therotating membrane assembly 18 at 32 and is measured by owmeter 34 inline 36. Middling brine pump 38 restores the pressure drop through therst stage membrane and returns the repressurized middling brine to thesaline water line 14. The rate of flow of middling -brine from membraneassembly 18 determines its saline concentration. Control of middlingbrine flow is effected by pump discharge valve 42 which reacts tosalinity meter 46 which measures the salinity of the product waterleaving the membrane assembly 18 through line 48.

Product water leaves the membrane assembly at outlet 68 andthe flow ismeasured by owmeter 50 in line 48. Product water is pumped from main 52by a distribution pump (not shown).

With further reference to FIGURE l, any precipitated salts which collectat the membrane surface as previously described are released from thebrine side of the lfirst and second stage membranes when the reverseosmotic flow is stopped momentarily. In the process of the presentinvention, water flow through the membranes is repeatedly interrupted bysuddenly increasing the water discharge pressure by rotating motorizedthree-Way valve 49 so that, simultaneously or sequentially, outlow ofwater is stopped and, at the same time or subsequently, high pressurewater from air-capped tank 51 is admitted through line 53 into productwater line 48 with the aid of compressor 55. Also, .just before closingvalve 49, middling brine outlet valve 33 is closed.

The water pressure in air-capped tank 51 is suicient to supplement theosmotic membrane pressure so that combined, `the total water pressure isequal to or greater than the brine pressure, thus momentarily stoppingthe reverse osmotic flow of water through the membranes.

Following the release of precipitated salts from the membranes asindicated above, the supply of water in aircapped tank 51 is replenishedthrough line 57 by means of pump 59.

If the three-way valve 49 is closed relatively slowly, water hammercontributes nothing to the pressure increase on the water side of themembranes. However, when a very short dwell of overpressure on the waterside of the membranes is desirable, the rapid closing of valve 49without admission of high pressure water could supply adequateinstantaneous pressure, provided that the extinguished velocity in line48 were of suficient magnitude as defined above.

Now referring to FIGURES 2 and 3, the structure and the internal fluidow of the rotating membrane assembly 18 are herebelow described:

Saline water raised to system pressure by system supply pump 8 entersthe rotating concentric membrane assembly 18 through axial inlet gland70. The saline water feed is radially distributed by two or morebalanced lines 72 and 74 to enter the annular space 54 between thepressure shell 56 and the primary cylindrical osmotic membrane 58.

Because, in the present example, 95 percent of the bn'nes salt isrejected by the osmotic membrane 58, the salinity of the Water forcedthrough membrane 58, through the water permeable, fiber reinforcedfilter paper 59 and through pervious support 60 into annular space '61has but two percent of the salinity of the brine in annular space 54.However, because the second and inner concentric osmotic membrane 62also rejects 95 percent of the salt from the water forced therethrough,the middling brine must increase in salinity. The maximum allowablesalinity of the middling brine in annular space 61 is determined bgy thespecifications of the product water as is shown in Table 1.

The removal of salt as middling brine from annular space 61 throughradial outlets 76 and 78 through axial gland is controlled Iby pumpdischarge valve 42 which reacts to the salinity of product water in line48, also as explained above.

The product water, forced through the second stage membrane 62, waterpermeable, fiber reinforced filter paper 63 and pervious support 64,leaves the central cylinder 65 through axial outlet 68 and product watergland 81 to be pumped from main 52, as explained above.

The rotating concentric membrane assembly 18 can be supported bytrunnion bearing 82 and by hoop rail 84 running on idlers 86 and bedriven by a pinion gear (not shown) engaging ring gear 88, or theassembly can lbe supported on two trunnion bearings and V-belt driven.

The brine pressure shell S6 is shown as cylindrical. However whensubstantial amounts of suspended solids enter with the saline waterfeed, it would be advantageous that the brine pressure shell be made inthe form of a truncated cone with the larger diameter at the brinedischarge end, in order to facilitate movement of the denser slurrycentrifugally held against the shell.

The ends 90 and 92 of the pressure shell are grcoved to accommodate thecylindrical membrane supports 60 and 64 in their sealing end gaskets.The ends are tightened against the gasketed membrane supports and thegasketed pressure shell 56 by the bolts 94 through lugs 96 which arewelded to the pressure shell or which may vbe made continuous of steelrods or bolts.

After assembly, the rotating device is statically and dynamicallybalanced by the adjustment of peripheral weight (not shown).

Because the novel method and apparatus of the present inventioneliminates the excessive accumulation of salts 1 1 against the osmoticmembrane surface at any Water flux or brine circulation rate, it becomesfeasible to use osmotic membrances which afford an incomparably largeeiective osmotic surface in proportion to the total volume of theapparatus employed. Obviously, the variety of configurations of membranesurface which can be utilized in accordance wtih the principles of thepresent invention is limitless.

Procedures are at hand for applying and/ or casting semi-permeablemembranes upon the outside of the pervious cylindrical support of thepresent invention. For exaccordance with the principles of the presentinvention. The figures includes in Table 1 and Table 14A .illustrateresults to be obtained when the product water is to have v 500 ppm. ofsalts. A- cellulose acetate osmotic membrane having a regularcross-sectional configuration and capable of 95% salt rejection at awater flux of 40 gal/ft.l2 day, kas described in UCLA Report 63-22, isused for each stage, with the feed brine containing 35,000 ppm. of sait.As will be seen from Table 1, the potable water yield volume (withymiddling brine excluded for purposes of simpliiication) is 31.0% of theincoming solution.

TABLE NO. 1.-TWO STAGE DESALINATION OF SALINE WATER BY REVERSE OSMOSISAS h/TODIFIED BY CENTRIPETAL ACCELERATION [Salt rejection, 95% permembrane stage] l Note: The figures set forth in this table have notbeen adjusted to take into account recycling of middling brine, in theinterests of simplification. Accordingly, the figures representapproximations only, but may be readily corrected by taking into accountthe dilution of feed brine at 35,000 ppm. salts with middling brine at10,000 p.p.m. salts.

ample, the formation of an osmotic membrane on the rotatable cylinder ofa centripetal accelerator within the contemplation of the presentinvention may be veffected by providing a water permeable, fiberglasspipe, such as is manufactured by the Amercoat Corporation at Brea,Calif, made smooth on its inside surface to thereby provide a completelysuitable cylindrical membrane ksupport on which a membrane (such as onemade of cellulose acetate) may be cast or otherwise placed. Thetemperature, time, materials, proportions and sequence of environmentsfor applying satisfactory membrane material to such a support aredisclosed, by Way of example, in U.S. patents 3,133,132 and 3,133,137(the disclosures of which are hereby incorporated by reference).

Another means of membrane support Vcan be provided by a metal,cylindrical support containing radially extending bores, groups of whichare circumferentially connected by peripheral, annular grooves less than1/16 inch wide and spaced apart about 1/2 inch, the grooves beingbridged by means of water permeable, ber reinforcedl filter paper orsome other stiff material and the membrane being placed on said filterpaper.

In the event that the solution from which water is being extractedyields some substance lighter than Water, which would tend to collect atthe membrane surface, a moditication of the rotatable membrane shapebecomes necessary. For example, in extracting water from sewageeffluent, certain compounds lighter than water, such as fats, waxes andoils, become centrifugally separated and must be continuously remo 'edfrom the membrane surface. For such service, the surface of themembrane, Lby suitable forming of the supporting assembly, is in theshape of a truncated cone with a slope about 1A. inch per foot inrelation to its axis of rotation. Also, at the smaller diameter end ofthe rotatable assembly, light media bleed tubes are provided for coaxialtake-oit, similar to the take-off ports shown in FlG. 2. When more thantrace amounts of constituents are mixed with the solution beingseparated, it is best to subject the feed stream to a centrifugingtreatment to remove such light constituents ahead of the membranesystem.

Table 1 and Table l-A set forth iigures for the carrying out of thetwo-stage desalination of saline water by reverse osmosis as modified bycentripetal acceleration in TABLE NO. 1-A.-THE TWO STAGE WINNING OFvPOTABLE WATER FROM THE SEA BY REVERSE OSMOTIC PRES- SURE BIODIFIED BYCENTRIPETAL ACCELERATION Primary Secondary Membrane Membrane Membranecharacteristics as set forth in the UCLA Report No. 63-22:

Casting Solutiorn. No. 1 No, 1 Membrane Heating Temperature, C 81. 8 81.8 Water Flux, GaL/ (Day) (Ft) when AP- A7r=750 psi., gal 40 40 SaltTransport Across Membrane Per Ft/ 4 Day, grains 6,140 1, 17o SaltRejection when Water Flux=40 Gall (Day) (Et), percent 95 95 Salinity ofFeed, ppm 35, 000 2, 625 Salinity of Discharge, ppm 52, 500 10, 000Salinity of Product, ppm. 2, 625 500 Feed Concentration Ratio 1% to 1 38 to 1 Middling Volume, Percent of Feed 38; 3 Potable Water Yield,Percent of Feed 31. 0

Osmotic Pressure, p.s.i 530 92 Overpressure due to Boundary LayerConcentration; C/C=1.1 when the Contripetal Acceleration is Greater than100 g., p.s.i 53 0 Membrane Pressure Drop at 40 Gah] (Day) (Ft) ReportNo. (i3-22, .AP-Ar, p.s.i 750 750 Brine Circulation (none), p.s. 0 0

Total Stage Pressure, p.s.i 1,333 S51 Equivalent Single Stage Pressure,1,333=

(851-l-O-383) =1,659 p.s.i.

Potable Water Yield from Sea Water per day for each Square Foot ofMembrane: 40/2=20 Gall (Day) (Ft).

Estimated Net Energy Requirement, less than 20 kwh. per 1,000 Gal. ofPotable Water.

Estimated Capital Investment: $0.25 per Gallon per Day oi Potable Waterfrom Sea Water.

from a common feed of saline Water. In this apparatus,

pressurized saline water enters rotating shaftr injection lgland 1ct) toiiow axially under self'aligning bearing 102, thence through a radialfeed injection manifold 104. From radial injection manifold 104 thesaline water enters the concentric brine chambers 106 and 108 throughopenings 110 and 112. Water substantially demineralized is forcedthrough cylindrically supported osmotic membranes 114 and 116 intoconcentric water chamber 118 and into central Water chamber 120. Productwater from concentric water chamber 118 is conducted around imperviousconcentric separator 124 and membranes 116 by product water by-pass 122.

The product water is bled from the assembly through axial port 128,thence through shaft outlet gland 130.

Saline water leaves the concentric brine chambers 106 and 108 throughmanifold 132, thence through axial outlet gland 136. Brine iiow throughthe concentric membrane assembly is balanced by adjusting valve 134.

A valve (not shown) downstream from the brine outlet brine outlet gland136 reacting to a salinity meter (not shown) reading product salinitylimits the brine concentration ratio.

As was the case with the pressure shell 56 of FIGURES 2 and 3, pressureshell 126 is shown as cylindrical but may be fabricated in the form of atruncated cone to facilitate movement of denser slurry centrifugallyheld against the shell if this is deemed desirable.

While FIGURE 4 does not illustrate any provision for the release ofsalts or other solids precipitated against the osmotic membranes (as wasthe case in the system of FIGURE 1), provision may be made for thispurpose if desired.

Table 2 sets forth operating data for an exemplary run of such a singlestage technique in accordance with the principles of the presentinvention, as applied to the desalination of brackish water.

TABLE No. 2.SINGLE STAGE REVERSE osMoTIC DE- SALINATION OF BRACKISHWATER AS lvIODIFIED BY CENTRIPETAL ACCELERA'IION [Salt rejection bymembrane, 98%] In order to further explain the operation of this invention, herebelow is described the three-stage desalination of seawater by three osmotic membranes in series as shown in Table No. 2.[Note: Semi-permeable membranes have been developed which reject as muchas 99 percent of the dissolved salt when a brine pressure is appliedgreater than the osmotic pressure. However, because such membranesusually include at least minor imperfections, the following example ofthe process of the present invention provides for the use of membraneswhich will reliably reject no more than 95 percent of the dissolvedsalt.] With reference to the three-stage flow sheet diagram of FIGURE 9and employing the apparatus shown in FIGURES 4 and 5 for each of thestages of the process, the Huid ow is traced as follows:

Sea water is forced by intake pump 200 over self-cleaning screen 202into surge tank and skimmer 204. From surge tank 204, first stage pump206 forces the sea water through line 208, through liowmeter 210 andinto the primary rotating concentric osmotic membrane assem bly 2.12 ofthe type shown in FIGURES 4 and 5 and previously described.

Salinity meter 213 reads the salinity of the water discharging from theprimary rotating membrane assembly through line 214 and operates brinedischarge control valve 215. Thus, the salinity of the primary dischargebrine C, for any given membrane characteristic, is a function vof thesalinity criterion of the feed stream to the secondary membraneassembly, Stage D, as shown in Table No. 2.

With continued reference to FIGURE 9, the partially desalinated waterleaves Stage C assembly 212 through 14 line 216 to flow through valve217 into surge tank 218.

Because the concentration of brine is highest in the primary osmoticassembly, salts, particularly gypsum, must be removed from the membranesurface by intermittently stopping the water ow through thesemi-permeable membrane. The procedure is as follows:

Valve 217 (see FIGURE 9) is operated to close line 216 and subsequentlyopen the line 216 to line 222. Thereupon, the water -in tank 224,pressurized by means of compressor 223, immediately raises the pressurein line 216 and on the water side of the primary semi-permeablemembranes in assembly 212 so that the back pressure supplied plus theosmotic pressure is momentarily greater than the brine pressure. Forexample, as shown in Table No. 2, the osmotic pressure across theprimary membranes between water containing 105,000 p.p.m. and 5,250parts per million of dissolved salts is approximately 1000 p.s.i.a. Ifthe total pumping pressure generated by primary pump 206 is, say, 1500p.s.i.a., tank 224 must be at a pressure of at least 500 p.s.i. in orderto halt the flow of water through the membrane and thereby releasingwhatever particulate material was so held against the membrane surface.(As explained earlier, a very fast pressure pulse of short duration canbe effected by closing valve 217 so rapidly that water hammer results.)

Following the release of whatever particulate matter was held againstthe membrane surface by momentarily back-flushing the membranes, valve217 is returned to its usual position and reverse osmosis resumes inassembly 212. At this point, the supply of water in air-capped tank 224is replenished through line 226 by means of pump 228.

The partially desalinated water leaving the Stage C assembly 212 atpractically atmospheric pressure enters second stage pump 230 throughline 232 and is raised in pressure suiciently (eg, to about 500-700p.s.i.) to overcome the approximately 400 p.s.i. osmotic pressurebetween outlet brine of Stage D (containing 36,400 p.p.m. of salt) andthe secondary product of Stage D (containing 1,820 p.p.m. of salt) [seeTable 2], plus the pressure drop of the system required for a reasonablel0 g.p.d./ft.2) water flux.

The partially desalinated water from Stage C (5,250 p.p.m.) enters thesecondary membrane assembly 234 (Stage D) through line 236 where it isconcentrated by reverse osmosis to the extent that the secondary productwater does not exceed 1,820 p.p.m. of salt. Salinity meter 238 reads thesalinity of the second stage product water in line 240.

Again, as was the case with the operation of Stage C, precipitated saltsare removed from the membranes in Stage D by means of air-capped tank241, line 234 and valve 244.

It should be noted that no brine at all leaves membrane Stage D throughvalve 242 until the salinity in line 240 rises to 1,820 p.p.m. of salt,as shown in Table No. 2. Likewise, in the primary Stage C, no brinepasses through valve 215 until the salinity in line 216 rises to 5,250p.p.m., also as shown in Table No. 2.

Product water from the Stage D assembly 234 (at about 1,820 p.p.m. ofsalt) leaves through line 240, valve 244 and into surge tank 246 atabout atmospheric pressure. This water enters Stage E pump 248 throughline 250 and is raised in pressure suiciently by pump 248 (e.g., toabout 150-300 p.s.i.) to overcome the approximately p.s.i. osmoticpressure between outlet brine E (containing l0,000 p.p.m. of salt) andthe secondary product of Stage E (containing 500 p.p.m. of salt) [seeTable No. 2], plus the pressure drop of the system required for areasonable (again, 10 g.p.d./ft.2) water ilux.

Stage D product water is forced into the Stage E assembly 252 throughYlines 254 where it is desalinated to the ultimately desired saltconcentration (e.g., 500 p.p.m.) by reverse osmosis as modified bycentripetal acceleration as previously described. v

15 Salinity meter 256 reads the salinity of the-product water in line258 and, as was previously the case, lno brine at all leaves the Stage Eassembly through valve 260 until the salinity in line 258 rises to 500ppm. of

TABLE NO.

celeration, vthe smaller is the increment of density necessary toinitiate convective movement Within the solution. Therefore, the higherthe centripetal acceleration to Which the solution is subjected, thelower is the limit to which the solution can be concentrated at theboundary layer. It follows that the ratio CW/Co is an inverse functionof centripetal acceleration. Y

As an example, the values of CW/C shown in FIGS. 7 and 8 for forcedconvection are obtainable with centripetal accelerations between 100 and400 times the acceleration of gravity, that is, a cylindrically mountedmembrane two feet in diameter, rotating at 541 r.p.m., subjects the mem-3.-THREE STAGE REVERSE OSMOTIC DESALINATION OF SALINE WATER .ASlVIODIFIED BY CENTRIPETAL ACCELERATION [Salt rejection, 95% permembrane] Brine C Brine D Brine E Product Water In Out In Out In OutSalt Concentration, p.p.1n 35, 000 105,000 250 36, 400 820 10, G00 /500Approximate Osmotic Pressure (110%), p.s.i.a 1, 000 400 100 BrineConcentrating Ratio 3/1 7/1 11/2 Fraction of Initial Saline Water Volume1 2% %i $6 67 3%1 Potable Water Yield, percent 46. 7

NoTE.-All brine is rejected in calculating the materials balance.

In the practice of the present invention, (1) the pumped pressure of thefeed solution'against the membrane surface and (2) the required speed ofrotation of the centripetal accelerator are determine as follows:

(1) Determination of pumped solution pressure.'- Using demineralizedwater as the initial feed, determine the pumping pressure necessary toobtain the required operating water flux rate,'which will give the iluidpres- `sure d-rop (PW) through the membrane when no solute is present.This demineralized water pumping pressure, added to theexperimentally-determined osmotic pressure (Pos) between solution andwater (an example of which is shown in FIG. 8), equals the total pumpingpressure which would obtain when CW/Cr-tl (where Co is the soluteconcentration in the bulk of the solution and CW is the soluteconcentration in the fluid lboundary layer at the membrane; see FIG. 7).

Obviously, if Cw/CfJ were to equal 1, that is, if there were noconcentration of solute at the membrane surface, the total pressureVwould be but slightly greater than the sum of the water pressure dropthrough the membrane and matte plus the osmotic pressure betweensolution and Vpure water. However, because the removal of Water fromsolution by passage through the semi-permeable membrane must, at leastmomentarily, effect some degree of concentration at the membranesurface, Cw/Co is al- Ways greater than unity.

For example, with reference to FIGURE 7, laminar solution flow past themembrane surface in the case of circular tubes, and at a water flux of40 gallons per square foot per day, results in a considerableVconcentration of solute at the membrane surface and CW/Co is seen to beas high as 10/1.

As is indicated in FIG. 8, the maximum osmotic pressure between brineand water is about 2000 p.s.i. and the limit of losXCW/Co is about 2000p.s.i.a. so long as precipitated salts do not actually cover themembrane, in which case the membrane maybe considered to be, in effectphysically blinded.

(2) Determination of centripetal acceleration and rotational speed asfunction of water flux- The rate of convective movement is dependentupon the magnitude of centripetal acceleration. Moreover, t-he greaterthe acbrane boundary layer to a centripetal acceleration of times theacceleration of gravity. Likewise, a rotational speed of 1082 r.p.m.applied to the same membrane would subject the membrane boundary layerto an acceleration, away from the membrane surface, of 400 times theacceleration of gravity.

The limit of centripetal acceleration is that at which the membrane andmatte would sutfer damage by tending to fly apart. However, such changefrom centrifugal force is not possible at any rotational speedcontemplated in the practice of this invention. For example, whenrotating at 1082 r.p.m., a two-foot diameter member and matte issubjected to a centrifugal force 40() times that of gravity. Since thematte and membrane weigh less than 14.4

pounds per square foot, or less than 1A@ pound per square inch, thecentrifugal force at 400 times the force of gravity is 40 pounds persquare` inch. However, the hydraulic pressure ofthe solution alwaysexerts a force many times greater than the centrifugal force. Therefore,centrifugal rupture of the membane and matte is impossible as long as acertain minimum solution pressure is maintained.

As an example of the foregoing, reference may be made to a three-stageconcentricrmembrane 'centripetal accelerator assembly as shown in FIGURE11. [Note: The structure shown in FIG. l1 has been illustratedschematically for ease of reference, onlythe pressure shell 308 and thethree semi-permeable membranes 310, 312 and 314 beingV shown] In thestructure of FIG. l1, membrane 310 has a diameter of two feet and anexposed surface area of 6.2 ft.2 per axial foot of cylinder, membrane534 a diamter of 11/2 feet and an exposed surface area of 4.7 ft.2/ ft.,and membrane 314 a diameter of one foot and an exposed surface area of3.1 ft. 2/ft. By rotation of the assembly at 1082 r.p.m. membrane 310 issubjected to a centripetal acceleration of 400G, membrane 312 to 300Gand membrane 314 to 200G.

FIGURE 7 is reproduced from page 44 of the 1963 Saline Water ConversionReport of the Department of the Interior and illustrates improvementsmade by the present invention upon the art of desalinating water byreverse osmosis. FIGURE 7 clearly points up the limitation of theprocess when the turbulent flow of brine past the membrane surface isrelied upon for control of boundary 1 7 layer salt buildup. The text ofthe 1963 Saline Water Conversion Report pertinent to FIGURE 7 follows:

The ordinate in figure 37 is the salt concentration adjacent to anosmotic membane divided by the salt concentration in the bulk liquidflowing past the osmotic membrane; the abscissa is the Reynolds numberof the ow. Turbulent ow of the brine in a tubular osmotic membrane andlaminar iiow of the brine in the channels between parallel stacks of hatosmotic membranes are included in the analysis. Curves are shown forseveral water uxes through the osmotic membrane and, for the laminarcase, two channel length/width ratios. At low water ux rates and highReynolds numbers, the salt buildup at the membrane surface is not great.But pumping cost considerations put practical limits upon the owReynolds number, and for practical Reynolds numbers, CW/Co can be ashigh as 2 for water flux rates of approximately g.p.d. per square foot,attainable with todays membranes. Since much research is currently beingdirected toward improving osmotic membrane capacities in order to reducemembrane costs, it is anticipated that membranes giving water tiux ratesof 40 to 100 g.p.d. per square foot will be developed. Figure 37 s-howsthat the problem of salt buildup at the membrane surface may -becomeincreasingly serious as better membrances become available. Since theosmotic pressure is approximately proportional to the saltconcentration, it is readily seen that large values of Cv,/Co willresult in higher operating pressures and greatly increased costs for thereverse osmosis process. t

FIGURE 7 also illustrates the marked advantage of using forcedconvection over a high lateral uid velocity for removing concentratedsolution from the membrane surface. As indicated, at a centripetalacceleration greater than 100G with zero solution velocity, the CW/Coratio is 1.5 or less at water uxes of up to 100. On the other hand,water uxes of this magnitude are not achievable with such low CW/Coratios even at extreme turbulent flow using conventional reverse osmosistechniques. The tremendous power economy and the significantly increasedmembrane life directly resulting from being able to use water fluxes ofgreat magnitude at relatively low or zero ow rates are immediatelyapparent from the foregoin.

For a clearer understanding of the principle of this invention, FIGURE 7is to be compared to FIGURE 10.

Because of the radial acceleration involved in the process of thepresent invention, any appreciable solute concentration at the boundarylayer results in an instant fluid imbalance. The induced velocity ofconvection is, of course, a direct function of the square of the angularvelocity of rotation of the cylindrical membrane assembly.

In the practice of this invention, the ratio of salt adjacent to themembrane to .the salt in the rejected Ibrine is an inverse function ofradial acceleration. This is illustrated in FIGURE l() where theestimated values of CW/CD are plotted against radial acceleration.Moreover, at radial accelerations in the order of 100 times gravity andabove, salt concentration in the boundary layer must rather closelyapproach the salt concentration in the bulk of the brine, even atextremely high water ilux values.

In lthe preceding discussion, a novel method of and `apparatus forwinning fresh water from saline solutions has been set forth. As will bereadily apparent from this discussion, however, the principles involvedin such method and apparatus are equally applicable to reverse osmosisprocesses involving any solute-containing solvent wherein it is desiredto decrease the concentration of solute in the solvent (or to increasesuch concentration, depending upon the desired product). For example,such principles are equally applicable to the recovery of water from rawsewage and to concentrate the putrescible substances into a relativelysmall stream in order to facilitate stabilization by conventional means.Similarly, the principles of the present invention are applicable to theseparation of solutions of light molecular weight from solutions ofgreater molecular weight. In such a process, the solution separator willbe constituted by a dialytic membrane and the solutions separated byreversed dialytic pressure modified by radial convection by means of thecentripetal acceleration technique of the present invention.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not rcstriCtiVe, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended 'to be embracedtherein.

What is claimed is:

1. In a process for the desalination of a saline solution wherein saidsaline solution is placed into contact with one side of a semi-permeablemembrane under a pressure greater than the osmotic pressure of saidsaline solution, the improvement comprising subjecting said salinesolution to acceleration greater than gravity in a direction away fromsaid one side of said membrane.

2. In a process for the diminution of the solute content of a solventwherein the solute-containing solvent is placed into contact with oneside of a semi-permeable membrane under a pressure greater than theosmotic pressure of said solute-containing solvent, the improvementcomprising subjecting said solute-containing solvent to accelerationgreater than gravity in a direction away from said one side of saidmembrane.

3. In a process in which a solute is removed from a solvent by bringingsaid solvent into contact with one side of an osmotic divider under apressure greater Ithan the osmotic pressure of said solvent, theimprovement comprising subjecting said solvent to suiicient centripetalacceleration to result in the convection of solvent increased in itsconcentration of said solute in a direction away from said one side ofsaid osmotic divider.

4. A process as defined in claim 3 wherein said process 1s a vapor gapreverse osmosis process and wherein said osmotic divider comprises avapor gap.

5. A process as defined in claim 3 wherein said process 1s a vapor gapreverse osmosis process and wherein said osmotic divider comprises ahydrophobic porous filter Vwhich is impermeable to water but permeableto water vapor, said uid being a saline solution.

6. A process as dened in claim 3 wherein said osmotic divider is asemi-permeable membrane permeable to said uid but substantiallyimpermeable to said solute.

7. In a process for the desalination of saline water wherein said salinewater is placed into contact with one side of a semi-permeable membraneunder a. pressure greater than the osmotic pressure `of said salinewater, the improvement comprising subjecting said saline water tosuicient centripetal acceleration to result in the convection ofconcentrated saline water in a direction away from said one side of saidmembrane.

8. In a process in which the solute concentration of a solvent isdiminished by bringing said solvent into contact with an osmotic dividerat a pressure in excess of the osmotic pressure of said solvent, theimprovement comprislng removing said solute from the effective osmoticdivider surface by forced convection through subjection of the systemcomprising said osmotic divider and solutecontaining solvent to radialacceleration in a direction away from said effective osmotic dividersurface.

9. A process as dened in claim 8 wherein said forced convection iscentpetally induced.

10. Apparatus for carrying out a process in which a solute is removedfrom a solvent by bringing said solvent into contact with one side oflan osmotic divider at a pressure in excess of the osmotic pressure ofsaid solvent, said apparatus comprising: an osmotic divider; means forbringing a solute-containing solvent to be subjected to` said processinto contact with one side of said osmotic divider'at a pressure inexcess of its osmotic pressure; means for withdrawing solvent diminishedin its content of said solute from the other side oi said osmoticdivider; and means for subjecting said solvent to sufficientVcentripetal acceleration to result in the convection of solventincreased in its concentration of said solute in a direction away fromsaid one side of said osmotic divider.

11. Apparatus as defined in claim additionally comprising a secondosmotic divider; means for bringing said solute-diminished solvent intocontact with one side of said second osmotic divider at a pressure inexcess of its osmotic pressure; means for withdrawing solvent stillyfurther diminished in its solute content than said solutediminishedsolvent from the other side of said second osmotic divider; saidacceleration-subjecting means also subjecting said solute-diminishedsolvent to acceleration greater than gravity in a direction away fromsaid one side of said second osmotic divider.

12. Apparatus for carrying out a process in which a solute is removedfrom a solvent by bringing said solvent into contact with one side of asemi-permeable osmotic membrane at a pressure in excess of the osmoticpressure of said solvent, said apparatus comprising: a semi-permeableosmotic membrane; means for bringing a solute-containing solvent to besubjected to said process into con tact with one side of said membraneat a pressure in excess of its osmotic pressure; means for withdrawingsolvent diminished in its content of said solvent from the other side ofsaid membrane; and means for subjecting said solvent to accelerationgreater than gravity in a direction away from said one side of saidmembrane.

13. Apparatus for carrying out a process in which Ysolute is removedfrom a solvent by bringing said solvent into contact with one side of anosmotic divider at a pressure in excess of the osmotic pressure of saidsolvent, said apparatus comprising: an annular osmotic divider; meansfor bringing la solute-containing solvent to be subjected to saidprocess into contact with the outer surface of said annular divider at apressure in excess of the osmotic pressure of said solvent; means forvinthdrawing solvent diminished in its content of said solute fromwithin the annulus of said osmotic divider; andmeans for rotating thesystem comprising said osmotic divider and said solute-containingsolvent about the axis of the annulus of said osmotic divider wherebysaid solvent may be subjected to suilicient centripetal acceleration toresult in the convection of solvent increased in its concentration ofsaid solute in a direction -away from the axis of said annulus.

14. Apparatus as deiined in claim 13 wherein said annular osmoticdivider is contained in a substantially cylindrical shell, the annularspace between the outer surface of said annular osmotic divider and theinner surface of said shell providing a path for movement of solvent.

15. Apparatus 'as deiined in claim 13 wherein a second annular osmoticdivider is positioned concentrically within said iirst mentioned annularosmotic divider so that said solvent diminished in its content ofsaid'solute will be subjected to further diminution in its solutecontent by passage `through said second osmotic divider; said rotatingmeans also being adapted to rotate said second osmotic divider Iaboutits axis.

16. A process for removing solute from a solvent comprising moving saidsolute-containing solvent along and in contact with one side of anosmotic divider at a pres- Vsure in excess of the osmotic pressure ofsaid solvent; and

simultaneously subjecting said solvent to acceleration r`greater thangravity in a direction away from said one side of said osmotic divider.

17. In a process in which solute is removed from a solvent by bringingsaid solvent into contact with one side of an osmotic divider at apressure greater than its osmotic pressure, the improvement comprisingsubjecting said solvent to suicient centripetal acceleration to resultin the convection of solvent increased in its concentration of saidsolute and suspended particulate matter contained therein in a directionaway from said one side of said osmotic divider. Y

18. In a process in which matter is removed from a liquid by bringingsaid liquid into contact with one side of an osmotic divider at apressure greater than its osmotic pressure and wherein solids accumulateat said one side of said osmotic divider during said process, theimprovement comprising subjecting said liquid to acceleration greaterthan gravity in a direction away lfrom said one side of said osmoticdivider, and at least at one point during said process and upon theaccumulation of solids at said one side of said osmotic dividerinterrupting the pressure drop across said osmotic divider so that thesum of the osmotic pressure of said liquid plus the liquid pressure onthe downstream side of said osmotic divider is at least as great ras thepressure on the liquid on said one side of said osmotic divider. Y

19. A process as deiined in claim 18 wherein said osmotic divider is anosmotic membrane.

20. A process as deiined in claim 19 wherein said pressure interruptionis effected by subjecting said osmotic membranes to water hammer by thesudden stoppage ofV flow of liquid away from the downstream side of saidosmotic membrane. Y

21. A process as defined in claim 18 wherein said pressure interruptionis eiected by subjecting said osmotic divider to water hammer by thesudden stoppage of ow of liquid away from the downstream side of saidosmotic divider.

r22. In a process in which solute is removed from a solvent, theimprovement comprising contacting solvent rst with one side of each ofat least two concentric osmotic dividers under a pressure greater thanthe osmotic pressure of the solvent, withdrawing relatively pure solventcontaining some solute from the other side of said iirst osmotic dividerinto an annular space separating said other side of said iirst osmoticdivider from one side of a second osmotic divider, -further purifyingsaid relatively pure solvent by maintaining said relatively pure solventlunder a pressure greater than the osmotic Ypressure of said relativelypure solvent and passing solvent containing less solute through saidsecond osmotic divider, simultaneous- Y ly subjecting said solvent andsaid relatively pure solvent `to suticient centripetal acceleration toresult in the convection of iluid increased in its concentration of saidsolute in a direction away from said one side of each of said osmoticdividers, and withdrawing solvent concentrated in solute from theannular space separating said osmotic dividers.

References Cited UNITED STATES PATENTS 2,411,238 11/1946 Zender 21o-222,678,133 5/1954 Thayer et al 210-360 2,692,854 10/ 1954 Henley 21Q-32 X3,129,146 4/ 1964 Hassler 210-22 X OTHER REFERENCES Ellis: FreshWater'Frorn the Ocean, by Cecil B. Ellis, The Ron-ald Press Co., NewYork, pages -76 relied upon (1953).

JOSEPH SCOVRONEK, Acting Primary Examiner.

MORRIS 0. WOLK, Examiner.

E. G. WHITBY, Assistant Examiner..

@man

UNTTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,355,382 November 28 1967 Morgan G. Huntington hat error appears in theabove numbered pat b certified t It 1S here y hat the said LettersPatent should read as ent requiring correction and t corrected below.

Column 4, line 32, "effect of such membrane inperfactior should readeffect of any such membrane imperfection line 34, "effect" should readaffect lines 60 and 69, "osmosic", each occurrence, should read osmosisColumn 7, line 11, after "Van't Hoff "i""' insert factor Column 8, line6, after "that the" insert greater the line 40, "at" should read asColumn 9, line 7, "ehe" should read the line 19, "hight" should readhigh line 29, after "pressure" insert of Column l0, line 73, "weight"should read weights Column l1, line 3, "membrances" should readmembranes Column l2, line 2, "includes" should read included TABLE No.l-A, first column, lines 27 and 28 thereof, "l 333= (851 0. 383)' shouldread 1 ,333 (851 O .383) Column 13 lines l5 and 16, cancel "brineoutlet", first occurrence. Column 14 line 40, after "Table" insert No.line 52, "234" should read 243 Column 16, line 41, "change" should readdamage line 62, "534" should read 312 Column 17, line 25, "membrances"should read membranes Column 20, line 28, "membranes" should readmembrane Signed and sealed this 23rd day of September 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents

1. IN A PROCESS FOR THE DESALINATION OF A SALINE SOLUTION WHEREIN SAIDSALINE SOLUTION IS PLACES INTO CONTACT WITH ONE SIDE OF A SEMI-PERMEABLEMEMBRANE UNDER A PRESSURE GREATER THAN THE OSMOTIC PRESSURE OF SAIDSALINE SOLUTION, THE IMPROVEMENT COMPRISING SUBJECTING SAID SALINESOLUTION TO ACCELERATION GREATER THAN GRAVITY IN A DIRECTION AWAY FROMSAID ONE SIDE OF SAID MEMBRANE.